1. Field of the Invention
The present invention generally relates to a technique for printing solder paste with use of a printing machine and mounting a component with use of an automatic mounter onto a printed wiring board including a board recognition mark, and particularly relates to a technique for properly mounting components on a printed wiring board including a component land covered with resist (hereinafter also referred to as an over resist type component land) and a component land not covered with the resist (hereinafter also referred to as a normal resist type component land) even if resist misalignment occurs.
2. Description of the Related Art
In recent years, printed wiring boards with “0603 size” small chip components mounted thereon have been increasing. The “0603 size” small chip components were developed in response to demand for components with smaller size and higher density, and have a size of 0.6 mm in length and 0.3 mm in width.
FIG. 8A shows a related art printed wiring board, wherein normal resist type component lands 5a and 5′ are exposed through resist openings 8a and 8′a having sizes greater than the component lands 5a and 5′a, respectively. Conductive patterns 17a and 18a are extending from the component lands 5a and 5′a, respectively.
If a resist printing mask (not shown) used for forming resist 2a is positioned rightward relative to a predetermined location, an area S2a of the conductive pattern 18a exposed through the right resist opening 8′a is larger than an area S1a of the conductive pattern 17a exposed through the left resist opening 8a. That is, the substantial area of the component lands 5a is not equal to the substantial area of the component land 5′a. 
Referring to FIG. 8C, when solder pastes 19a and 20a printed on such component lands 5a and 5′a are heated and melted by a reflow machine, a chip component 15a as small as the “0603 size” chip components might be pulled toward the component land 5′a having the larger substantial area and be partly lifted.
Referring then to FIG. 8B, to avoid such mounting failure, component lands 6a and 6′a having the same area by covering peripheries of conductive foils 22a and 22′a with the resist 2a are formed with an over resist method. The component lands 5a and 5′a formed by a normal resist method and the component lands 6a and 6′a formed by the over resist method are present on the same printed wiring board.
When a normal resist type component land and an over resist type component land are present on a printed wiring board, printing misalignment and mounting misalignment might occur for the following reasons.
The reasons of the occurrence of the printing and mounting misalignment are described with reference to a printed wiring board 1a of FIG. 5 including a board recognition mark 3a formed with the normal resist method, wherein rightward and downward misalignment of the resist 2a exists.
A resist printing mask (not shown) is placed on the printed wiring board 1a including the board recognition mark 3a, the normal resist type component land 5a, and the over resist type component land 6a. The resist 2a is applied onto the printed wiring board 1a through the mask.
The resist opening 8a for the normal resist type component land 5a has a size large enough to accommodate the maximum resist misalignment resulting from misalignment between the printed wiring board 1a and the mask, so as to prevent the component land 5a from being covered with the resist 2a. Accordingly, the center point of the component land 5a is not affected by the resist misalignment, so that the positional relationship between the center point of the component land 5a and a center point 10a of the board recognition mark 3a is consistent with the design value of the printed wiring board 1a. 
On the other hand, since the center point of the over resist type component land 6a is defined by the center point of a resist opening 9a, the center point of the component land 6a is displaced from a predetermined center point of the component land 6a by an amount corresponding to the resist misalignment.
This displacement is equal to the displacement ΔX, ΔY between the center point 10a of the board recognition mark 3a and a center point 11a of a resist opening 4a. 
With reference to FIG. 6, in a process of mounting chip components 15a and 16a onto the printed wiring board 1a having the configuration as described above, solder pastes 13a and 14a are printed onto the component land 5a and 6a, respectively, of the printed wiring board 1a through a screen mask (not shown) with use of a printing machine.
More specifically, the printing machine captures an image of a recognition mark (not shown) of the screen mask with use of a CCD camera or the like so as to detect the center point of the recognition mark. The printing machine then captures an image of the board recognition mark 3a of the printed wiring board 1a so as to detect the center point 10a of the board recognition mark 3a. 
The misalignment between the center point of the recognition mark of the screen mask and the center point 10a of the board recognition mark 3a of the printed wiring board 1a is corrected, so that openings of the screen mask are aligned with the corresponding component lands 5a and 6a. Then, the solder pastes 13a and 14a are printed onto the component lands 5a and 6a, respectively, through the corresponding openings of the screen mask.
The openings of the screen mask corresponding to the component lands 5a and 6a are formed based on design data of the printed wiring board 1a. Therefore, although the solder paste 13a is aligned with the normal resist type component land 5a, the solder paste 14a is misaligned with the over resist type component land 6a by ΔX, ΔY.
Accordingly, printing position correction is required to equalize the amount of printing misalignment of the over resist type component land 6a to the amount of printing misalignment of the normal resist type component land 5a. 
The following briefly describes a process of mounting the chip components 15a and 16a onto the component lands 5a and 6a, respectively, with use of an automatic mounter with reference to FIG. 7.
Before mounting the components 15a and 16a, the automatic mounter captures an image of the board recognition mark 3a of the printed wiring board 1a with use of the CCD camera or the like so as to detect the center point 10a of the board recognition mark 3a. 
The automatic mounter then mounts the component 15a in a position spaced apart from the center point 10a by a distance (L1, W1), and the component 16a in a position spaced apart from the center point 10a by a distance (L2, W2).
The distance L1, W1 is from the center point 10a of the board recognition mark 3a to the midpoint between conductive foils forming the normal resist type component lands 5a and 5′a, while the distance L2, W2 is from the center point 10a of the board recognition mark 3a to the midpoint between the conductive foils 22a and 22′a forming the over resist type component lands 6a and 6′a. These distances L1, W1 and L2, W2 are defined in a design specification of the printed wiring board 1a, and are registered in advance in a database together with the corresponding components 15a and 16a. 
Therefore, although the component 15a is aligned with the normal resist type component lands 5a and 5′a without misalignment, the component 16a is misaligned with the over resist type component lands 6a and 6′a by ΔX, ΔY.
Accordingly, mounting position correction for equalizing the amount of misalignment of the over resist type component 16a and the amount of misalignment of the normal resist type component 15a or mounting position correction for correcting the misalignment of the over resist type component 16a is required.
Patent Document 1 discloses a technique for avoiding such problems. According to Patent Document 1, in addition to a recognition mark formed of conductive foil, a second mount recognition mark covered with resist is formed when the resist is applied for partially covering an over resist type component land. The first mount recognition mark formed of the conductive foil is used for mounting a component onto a normal resist type component land, and the second mount recognition mark covered with the resist is used for mounting a component onto the over resist type component land. Thus, the components are mounted on the corresponding component lands without misalignment.
However, because only one of the mount recognition marks can be detected during a solder paste printing process, one of the component lands is misaligned with the solder paste. Therefore, printing position correction is required.
<Patent Document 1> Japanese Patent Laid-Open Publication No. 11-40907
As can be understood from the above description, with the above-described related art techniques, if a component land covered with resist and a component land not covered with the resist are present on the same printed wiring board, misalignment between solder pastes and corresponding component lands and misalignment between components and the corresponding component lands due to resist misalignment cannot be avoided.